Catalytic activity of haemin. Influence of dissolution conditions on activity

Robson

Brown

1973

Self Cite

1. The variation of the specific stoicheiometric catalatic activity of proto- and deuteroferrihaem with total ferrihaem concentration has been studied at 25 degrees C over a wide range of pH. For deuteroferrihaem the results imply that only monomeric ferrihaem species contribute significantly to the catalatic activity. Protoferrihaem is more highly dimerized in solution and, in this system, contributions to the catalatic activity from both monomeric and dimeric ferrihaem species were observed. The ratio of the specific activity of protoferrihaem monomer to that of dimer varied from approximately 20 at pH7 to 5x10(4) at pH12.2. 2. The specific activity of protoferrihaem monomer closely resembles that of deuteroferrihaem monomer, both in magnitude and pH-dependence. In both cases the activity is inversely proportional to [H(+)]. In contrast, the activity of catalase is independent of pH in the range 5-10. At pH13 the activity of ferrihaem monomer becomes equal to the maximal activity of catalase. The results are in good agreement with those reported by Brown et al. (1970b) and provide support for the assumptions upon which this previous analysis relied. 3. Information from the literature concerning the catalatic activity and dimerization of the iron(III) complex of 4,4',4'',4'''-tetrasulphophthalocyanine (Waldmeier & Sigel, 1971; Sigel et al., 1971) have been re-analysed. The results imply that both the monomeric and dimeric complexes contribute to catalatic activity and these activities closely resemble those of the corresponding protoferrihaem species.

Section: Methodsmentioning

confidence: 99%

The catalase activity of ferrihaems

Robson

Brown

1973

Self Cite

“…The specification and methods of assay of materials have been described previously (Brown et al, 1970b;Jones et al, 1973). Deuteroferrihaem solutions were prepared by method A (Brown et al, 1970c). Kinetic spectrophotometric studies were made at 25°C, I = 0.1 (added electrolyte NaCl) in a Durrum-Gibson D-1 10 stopped-flow spectrophotometer.…”

Section: General Methodsmentioning

confidence: 99%

Oxidation of deuteroferrihaem by hydrogen peroxide

Prudhoe

Robson

1973

Self Cite

1. The oxidation of deuteroferrihaem by H(2)O(2) to bile pigment and CO was studied both by stopped-flow kinetic spectrophotometry and mass spectrometry, at 25 degrees C, I=0.1m. 2. Spectrophotometric studies imply that, at constant pH, the rate of bile pigment formation is first-order with respect to [H(2)O(2)] and also proportional to [deuteroferrihaem monomer]. The effect of pH on the apparent second-order rate constant suggests that acid-ionization of deuteroferrihaem monomer is important in the reaction mechanism. 3. The relative rates of formation of O(2) (from catalytic decomposition of H(2)O(2)) and CO (from oxidation of ferrihaem) have been measured by mass spectrometry. The results are in excellent agreement with those obtained by combining kinetic data for catalytic decomposition (Jones et al., 1973, preceding paper) with the spectrophotometric results for deuteroferrihaem oxidation.

“…1). Measured activities were reproducible with both methods and the results may therefore be used comparatively, although the origin of the effect is not understood (Brown et at. 1970c).…”

Section: Methodsmentioning

confidence: 99%

“…Although there are several points of kinetic similarity with aquairon(III) ion and catalase, no detailed basis for a qualitative or quantitative comparison including ferrihaem has been established. Features that complicate the intimate study of ferrihaem catalysis include autoxidation of protoferrihaem (Brown et al 1968), catalyst destruction by the substrate (Brown & Jones, 1968a), variation of catalyst properties with conditions of dissolution (Brown, Dean, Jones & Kremer, 1970c), dimerization and variations in the protolytic state of ferrihaem in aqueous solution (Brown, Dean & Jones, 1970b;Brown, Jones & Lantzke, 1969).…”

mentioning

confidence: 99%

Catalatic activity of iron(III)-centred catalysts. Role of dimerization in the catalytic action of ferrihaems

Brown

Dean

1970

Self Cite

1. The specific stoicheiometric catalatic activity of deuteroferrihaem is 10-100-fold greater than that for protoferrihaem, depending on pH. It is suggested that the difference in activity may be related to quantitative differences in the extent of dimerization in aqueous solutions of proto- and deutero-ferrihaem (Brown, Dean & Jones, 1970b). 2. A quantitative comparison of the kinetic and equilibrium data implies that the catalytic activities of ferrihaems are determined by the proportion of monomer present. The specific activity of ferrihaem monomer calculated varies inversely with H(+) ion concentration and attains a value equal to the maximal activity of catalase at pH>pK(a)(H(2)O(2)). 3. A comparison of catalatic behaviour in the series of iron(III)-centred catalysts aqua-iron(III) ion, ferrihaem monomer and catalase suggests that the unique feature of catalase action resides in the pH-independence of the reaction.